Libelium Waspmote Manual page 34

Real application example
After connecting the sensor, you only have to upload one of the example codes included in the Waspmote IDE, for instance the
example number one:
http://www.libelium.com/development/waspmote/examples/4-20ma-01-current-loop-basic-example
In the serial monitor you should see that the sensor is transmitting 4 mA. The 4 mA "bottom of span" signal allows the receiver
to detect a broken wire or failed instrument. Remember that in normal operation, a 4-20 mA sensor delivers between 4 and
20 mA. Any current above or below means malfunction.
The constant-current feature of a current loop cancels out voltage drop errors due to long wiring runs (of course this would also
be true if you selected different current values for zero and span [e.g., 5-30 mA]).
Figure : Data reception from the 4-20 mA sensor
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